Radio resource control method in mobile communication system, and mobile communication system

ABSTRACT

The invention relates to a radio resource control method, a mobile communications system and a network element implementing the method. According to the invention, the cell change procedures performed by the user equipment in an idle state are controlled dynamically with control information that is adjusted according to a predetermined time pattern. The invention enables for instance an advanced cell change in an idle state, thus reducing the probability of a handover while the user equipment is in a dedicated connection to the network.

FIELD

The invention relates to a radio resource control method in a mobilecommunication system, and to a mobile communication system.

BACKGROUND

As the need for transferring large amounts of information, such as dataassociated with video and audio signals, over wireless communicationsystems has increased, handover procedures where user equipment movesfrom a cell to another may introduce a significant decrease in theeffective capacity of the system. This is especially the case when thehandover occurs between cells with different radio interfaces. Thedifference between the radio interfaces may be due to different carrierfrequencies or different radio access technologies between the cellsparticipating the handover.

The handover may occur in different states of the radio resourcecontrol. Such states include a connected state in which the userequipment is allocated a dedicated channel, and an idle state in whichthe user equipment is not allocated a dedicated connection. Commonchannels, such as common pilot channels and common broadcast channels,are in turn used in idle states.

In an idle state, the user equipment is capable of carrying out cellchange procedures aimed at selecting a cell which the user equipment cancamp on after leaving the serving cell. The cell change procedures arecontrolled by the network using control information for the cell changeprocedures. The control information associated with the cell change inan idle state is broadcast to the user equipment via control channels ofthe radio system.

According to prior art solutions, the control information associatedwith the cell change procedures is typically based on fieldmeasurements, and the control information is fed in the system duringthe network set-up. The prior art solutions can lead to a situation,where the user equipment camps on a cell with a limited optimisationlevel, thus increasing the probability for handover during a dedicatedconnection and data transfer. As a result, the capacity of the radiosystem is decreased due to simultaneous signalling and data transfer.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the invention to provide a method and a mobilecommunication system in such a way that the cell change procedures canbe controlled dynamically while the user equipment is in an idle state.This is achieved by a radio resource control method in a mobilecommunication system comprising a serving cell formed by a serving basestation, at least one neighbour cell formed by a neighbour base station,and user equipment capable of receiving signals from said base stations,the method comprising the steps of; camping, in an idle state, on theserving cell; receiving, in the user equipment, control information forcontrolling cell change procedures of the user equipment, said cellchange being conducted from the serving cell to a target cell; andperforming, in the user equipment, the cell change procedures based onthe received control information. In a method according to theinvention, at least one element of said control information is adjusted,before the control information is received, according to a predeterminedtime pattern, thus forming adjusted control information; and the cellchange procedures are controlled based on said adjusted controlinformation.

The invention also relates to a mobile communication system comprising anetwork part for providing the fixed infrastructure of the mobilecommunication system; the network part comprises a serving base stationfor forming a serving cell; the network part comprises a neighbour basestation for forming a neighbour cell; a user equipment comprisingreceiving means for receiving signals from the serving base station andfrom the neighbour base station; the network part comprises a controlmeans for controlling cell change procedures with control information,said cell change being conducted from the serving cell to a target cell;the user equipment comprises cell change procedure means for performingcell change procedures based on control information received from thenetwork part; and the receiving means and cell change procedure meansare configured to camp on the serving cell in an idle state. In a mobilecommunication system according to the invention, the network partfurther comprises adjusting means for adjusting at least one element ofsaid control information according to a predetermined time pattern, thusforming adjusted control information.

Preferred embodiments of the invention are described in the dependentclaims.

The method and system of the invention provide several advantages. In apreferred embodiment of the invention, the cell change procedure can becontrolled such that the probability of a cell change is lowered whilethe user equipment is in a dedicated connection, thus reducing mobilemeasurements and signalling during a dedicated connection and increasingthe overall capacity of the mobile communication system.

LIST OF THE DRAWINGS

In the following, the invention will be described in greater detail withreference to the preferred embodiments and the accompanying drawings, inwhich

FIG. 1 shows a simplified structure of a mobile communication system bymeans of a block diagram;

FIG. 2 illustrates an example of a cell structure;

FIG. 3 illustrates an example of a cell structure;

FIG. 4 illustrates different states of the radio resource control;

FIG. 5 illustrates embodiments of the invention by means of a graphicalrepresentation;

FIG. 6 shows a preferred embodiment of the invention by means of a flowchart;

FIG. 7 shows a second preferred embodiment of the invention by means ofa flow chart;

FIG. 8 shows a third preferred embodiment of the invention by means of aflow chart;

FIG. 9 shows a fourth preferred embodiment of the invention by means ofa flow chart; and

FIG. 10 shows an example of a structure of user equipment.

DESCRIPTION OF THE EMBODIMENTS

The invention can thus be applied to a mobile communication systemcomprising more than one radio access technology to which the userequipment can be connected. The radio access technologies that can beused include: GSM (Global System for Mobile Communications), GERAN(GSM/EDGE Radio access network), GPRS (General Packet Radio Service),E-GPRS (EDGE GPRS), UMTS (Universal Mobile Telecommunications System),CDMA2000 (CDMA, Code Division Multiple Access), US-TDMA (US TimeDivision Multiple Access), Bluetooth-based short-range systems and WLAN(Wireless Local Area Network). Below, preferred embodiments will bedescribed using two radio systems, i.e. the GSM and UMTS, as examples,without limiting the invention to these systems, as will be obvious to aperson skilled in the art.

With reference to FIG. 1, let us examine an example of a mobilecommunication system to which the preferred embodiments of the inventioncan be applied. FIG. 1 is a simplified block diagram which illustratesthe most important parts of mobile communication systems at networkelement level. The structure and the functions of the network elementsare only described when relevant to the invention.

The main parts of a mobile communication system are a core network (CN)100, a radio access network 130 and user equipment (UE) 170. The userequipment 170 has a radio interface 168 with the core network 100. Aradio access network (RAN) called UTRAN (UMTS Terrestrial Radio AccessNetwork) 130 belongs to the third generation and is implemented bywideband code division multiple access (WCDMA) technology. FIG. 1 alsoshows a base station system 160 implemented by time division multipleaccess (TDMA) technology, and an Internet Protocol Radio Access Network150 (IP RAN) implemented with WCDMA technology.

On a general level, the mobile communication system can also be definedto comprise user equipment 170 and a network part 122. The userequipment 170 is also called a terminal, a mobile station, a subscriberterminal and a mobile telephone. The network part 122 comprises thefixed infrastructure of the radio system, i.e. the core network 100, theradio access network 130 and the base station system 160. In thiscontext, the radio access network 130, the base station system 160, theInternet protocol radio access system 150, and related systems will becalled a radio access network. Furthermore, for the sake of simplicity,the core network 100 is shown in terms of 2G network elements.

The structure of the core network 100 corresponds to a combinedstructure of the GSM and GPRS systems. The GSM network elements areresponsible for establishing circuit-switched connections, and the GPRSnetwork elements are responsible for establishing packet-switchedconnections; some of the network elements are, however, included in bothsystems.

A mobile services switching centre (MSC) 102, or an MSC server (MSS), isthe centre point of the circuit-switched side of the core network 100.The same mobile services switching centre 102 can be used to serve theconnections of the radio access network 130, the base station system160, and the Internet protocol radio access system 150. The tasks of themobile services switching centre 102 include: switching, paging, userequipment location registration, handover management, collection ofsubscriber billing information, encryption parameter management, andecho cancellation.

The number of mobile services switching centres 102 may vary: a smallnetwork operator may only have one mobile services switching centre 102but large core networks 100 may have several ones. Large core networks100 may have a separate gateway mobile services switching centre (GMSC)110, which is responsible for circuit-switched connections between thecore network 100 and external networks 180. The gateway mobile servicesswitching centre 110 is located between the mobile services switchingcentre 102 and the external networks 180. An external network 180 can befor instance a public land mobile network (PLMN) or a public switchedtelephone network (PSTN). The public land mobile network (PLMN) 180 is apublic provider of mobile communication services, usually maintained andmanaged by administrative authorities or a recognized private operatingagency (RPOA). For the sake of simplicity, the administrative authorityor RPOA operating PLMN is called a network operator or an operator. PLMNmay rely on several radio access technologies, e.g. UTRA, GSM, and theInternet protocol radio access based technologies.

A home location register (HLR) 114 comprises a permanent subscriberregister, i.e. the following information, for instance: an internationalmobile subscriber identity (IMSI), a mobile subscriber ISDN number(MSISDN), an authentication key, and when the radio system supportsGPRS, a packet data protocol (PDP) address.

A visitor location register (VLR) 104 contains roaming information onuser equipment 170 in the area of the mobile services switching centre102. The visitor location register 104 comprises almost the sameinformation as the home location register 114, but in the visitorlocation register 104, the information is kept only temporarily. Thevisitor location register 104 comprises information needed forprocessing calls placed or received by user equipment 170 registered ina database of the visitor location register 104. The visitor locationregister 104 may also receive the necessary additional information fromthe home location register 114. The visitor location register 104comprises the following information, for example: an internationalmobile subscriber identity (IMSI), a mobile subscriber ISDN number(MSISDN), user equipment roaming number (MSRN) and the location area(LA) of a user equipment.

An equipment identity register (EIR) 112 comprises the internationalmobile equipment identities (IMEI) of the user equipment 170 used in theradio system, and a so-called white list, and possibly a black list anda grey list.

An authentication centre (AuC) 116 is always physically located in thesame place as the home location register 114, and it comprises asubscriber authentication key and a corresponding IMSI.

The network elements shown in FIG. 1 are functional entities whosephysical implementation may vary. Usually, the mobile services switchingcentre 102 and the visitor location register 104 constitute one physicaldevice while the home location register 114, equipment identity register112 and the authentication centre 116 constitute another physicaldevice.

A serving GPRS support node (SGSN) 118 is the centre point of thepacket-switched side of the core network 100. The main task of theserving GPRS support node 118 is to transmit and receive packetstogether with the user equipment 170 supporting packet-switchedtransmission by using the radio access network 130, the base stationsystem 160, or the Internet protocol radio access system 150. Theserving GPRS support node 118 contains subscriber and locationinformation related to the user equipment 170.

A gateway GPRS support node (GGSN) 120 is the packet-switched sidecounterpart to the gateway mobile services switching centre 110 of thecircuit-switched side with the exception, however, that the gateway GPRSsupport node 120 must also be capable of routing traffic from the corenetwork 100 to external networks 182, whereas the gateway mobileservices switching centre 110 only routes incoming traffic. In ourexample, the external networks 182 are represented by the Internet.

The base station system 160 comprises a base station controller (BSC)166 and base transceiver stations (BTS) 162, 164. The base stationcontroller 166 controls the base transceiver station 162, 164. Inprinciple, the aim is that the devices implementing the radio path andtheir functions reside in the base transceiver station 162, 164 whilecontrol devices reside in the base station controller 166.

The base station controller 166 is responsible for the following asks,for instance: radio resource management of the base transceiver station162, 164, inter-cell handovers, frequency control, i.e. frequencyallocation to the base transceiver stations 162, 164, management offrequency hopping sequences, time delay measurement on the uplink,implementation of the operation and maintenance interface, and powercontrol. The radio resource management includes e.g. the cell changeprocedures.

The base transceiver station 162, 164 comprises at least one transceiverwhich implements one carrier, i.e. eight time slots, i.e. eight physicalchannels. Typically, one base transceiver station 162, 164 serves onecell, but a solution is also possible wherein one base transceiverstation 162, 164 serves several sectored cells. The tasks of the basetransceiver station 162, 164 include, for example: calculation of timingadvance (TA), uplink measurements, channel coding, encryption,decryption, and frequency hopping.

The radio access network 130 comprises radio network subsystems 140.Each radio network subsystem 140 comprises radio network controllers(RNC) 146 and nodes B 142, 144. Node B is a rather abstract concept; theterm ‘base transceiver station’ is often used instead.

Operationally, the radio network controller 146 correspondsapproximately to the base station controller 166 of the GSM system, andnode B 142, 144 corresponds approximately to the base transceiverstation 162, 164 of the GSM system. Solutions also exist in which thesame device is both the base transceiver station and node B, i.e. thedevice is capable of implementing both the TDMA and WCDMA radiointerfaces simultaneously.

The Internet Protocol Radio Access Network 150 comprises at least oneInternet protocol base station (IP BTS) 158. The Internet Protocol RadioAccess Network 150 also comprises a circuit-switched gateway (CSGW) 156,RAN gateway (RNGW) 154, and RAN access server (RNAS) 152. Thecircuit-switched gateway 156 is a logical element used between theInternet Protocol Radio Access Network 150 and the circuit-switchednetwork elements of the core network 100. The circuit-switched gateway156 is controlled by the RAN access server 152. The RAN access server152 acts as a signalling gateway between the Internet Protocol RadioAccess Network 150 and the core network 100. The RAN gateway 154 is theInternet protocol user plane from the core network 100 or other radioaccess network 130 to the Internet Protocol Radio Access Network 150.The internet protocol base station 158 can be viewed as a small RNC/BTCconnected to the RAN access server 152 and the gateways 154, 156. In theInternet Protocol Radio Access Network 150, most of the functions of thecentralised controllers, such as radio network controller 146 and thebase station controller 166, are moved to the IP base station 158.

In this context, the node B 142, 144, base transceiver stations 162, 164and the Internet protocol base station 158, and the correspondingnetwork elements of other relevant radio systems will be called a basestation unless otherwise indicated. Furthermore, the network controller146, the base station controller 166 and other elements performingsimilar tasks will be called a base station controller unless otherwiseindicated. The network controller can be located in the base stationthat the network controller controls.

The user equipment 170 comprises two parts: mobile equipment (ME) 172and a UMTS subscriber identity module (USIM) 174. In an embodiment, theuser equipment 170 comprises an identity module 174 for each radiosystem, to which the user equipment 170 can be connected. The userequipment 170 comprises at least one transceiver for establishing aradio link to the radio access network 130 or base station system 160.The user equipment 170 further comprises an antenna, a user interfaceand a battery.

USIM 174 comprises user-related information and information related toinformation security in particular, for instance, an encryptionalgorithm.

The mobile communication systems according to the invention can bedesigned using hierarchical cell structures (HCS) or non-hierarchicalcell structures (non-HCS). An example of a hierarchical cell structure200 is shown in FIG. 2. The hierarchical cell structure 200 consists ofat least two cells 210, 220, 230, 240, 250, 260, and 270, which can beprioritised with different priorities. The prioritising is included inthe prioritising information that can be delivered to the user equipment170 in system information, for example. In general, the cellprioritisation is a means of encouraging the user equipment 170 toselect some suitable cells in preference to others. Operators may prefera certain type of cell not to be selected unless if it is the onlysuitable type. For example, umbrella cells 210 can be preferred due totheir large frequency reuse distance. Micro-cells 220, 230, 240, orpico-cells 250, 260, 270 can be preferred due to their high capacity.Different cells 210 to 270 can be created using different frequencies.However, different frequencies can also be used in the cells of the samehierarchical level in order to cope with a high load in the system, forexample.

In a non-hierarchical cell structure, the priorities between the cellsare irrelevant. In general, a non-hierarchical cell structure mayconsist of cells of different radio access networks, cells of networksof different PLMNs, and cells of different radio systems. In the presentcontext, only the cells are relevant that the user equipment 170 can beconnected to.

With reference to FIG. 3, let us consider a simplified mobilecommunication system, the network part 122 of which comprises a servingbase station 312 controlled by a serving base station controller 314.The serving base station 312 forms a serving cell 310, which the userequipment 170 has camped on. Furthermore, the network part 122 comprisesa neighbour base station 322 controlled by a neighbour base stationcontroller 324. The neighbour base station forms a neighbour cell 320.The network elements shown in FIG. 3 correspond those shown in FIG. 1.The user equipment 170 is configured to receive signals from both theserving base station 312 and from the neighbour base station. Also, thecarriers of the neighbour cell 320 can be listed in the neighbour listof the user equipment 170. The user equipment 170 is configured toreceive control information 316 for controlling the cell change from theserving base station 312. The serving cell 310 and at least oneneighbour cell 320 constitute a group of cells from which a new servingcell, called a target cell, is selected in the cell change procedurebased on the received control information.

When camped on a cell, the user equipment 170 has completed a cellchange process and has chosen a cell from which it plans to receiveservices. When camped on the cell, the user equipment 170 receivescontrol information from the serving cell 310 for controlling the cellchange procedures of the user equipment 170. Receiving the controlinformation includes the selecting and monitoring of paging channels,such as PICH (page indicator channel) and PCH (paging channel) broadcastin the serving cell 310; monitoring relevant system information and cellbroadcast messages including the control information for controlling thecell change procedures. The system information can also indicate whethera hierarchical of non-hierarchical cell structure is used. When campedon the cell, the user equipment 170 is capable of performingmeasurements on the surrounding cells on the purpose of carrying out thecell change procedures.

With reference to FIG. 4, let us consider different states of radioresource control (RRC) of the user equipment 170 and the associatedtransitions between the different states. The main states of the radioresource control are idle states 412 and connected states 414.

In the idle states 412, the user equipment 170 has neither radioconnection nor logical connection to the network part 122. However, theuser equipment 170 is capable of receiving control information, such assystem information and cell broadcast messages, from the serving cell310. The system information comprises elements, such as qualitythresholds, quality offsets, temporary quality offsets, and penaltytime, which can be used in the cell change procedures and which can beadjusted according to the predetermined time pattern. With the controlinformation, the radio resource control of the user equipment 170 may,for example, ask the physical layer of the user equipment 170 to performcertain radio measurements on signals transmitted from the relevantcells. Such signals are transmitted for example via control channels,such as common and paging channels.

In UMTS, the idle states 412 comprise the idle mode 400, and the listedsub-states of the connected mode 402: CELL_FACH (FACH, Forward AccessChannel) state 406, CELL_PCH (PCH, Paging Channel) state 408, andURA_PCH (URA, UTRAN Registration Area) state 410.

The connected states 414 comprise a CELL_DCH 404 state (DCH, DedicatedTraffic Channel) representing an active state of the radio resourcecontrol, in which a dedicated connection to both transmission directionsis allocated to the user equipment 170. This state corresponds to acircuit-switched connection.

In a preferred embodiment of the invention, the user equipment 170 campson the serving cell 310 in one of the following idle states 412specified in the 3GPP specifications: idle mode 400, CELL_FACH state406, URA_PCH state 410, CELL_PCH state 408.

The CELL_FACH state 406 has no dedicated traffic channel (DCH), but datacan still be transferred via common channels. This state is particularlysuitable for packet-switched connections. The use of common channelspreserves the radio resources of the cell. In the uplink direction,small data packets and control signals can be sent on RACH (RandomAccess Channel) or CPCH (Common Packet Channel). In the downlinkdirection, FACH (Forward Access Channel) can be used for transmittingcontrol information for controlling the cell change procedures. However,the CELL_FACH state 406 is not a favourable state in terms of powerconsumption since the user equipment 170 has to monitor control thechannels, such as the FACH channel continuously. Consequently, if thereis no data transmission activity for a certain time, RRC moves from theCELL-FACH state over to the CELL_PCH 408 state.

The CELL_PCH state 408 is in many respects like the idle mode 400, sincethe paging channels are monitored by the user equipment 170. The systeminformation and the cell broadcast messages are also received. Thedifference is that RRC connection still exists logically in the CELL_PCHstate. The RRC moves back to the CELL_FACH state if any uplink access isinitiated, or if a paging message is received. This is because noup-link activity is possible in the CELL_PCH state.

In the URA_PCH state 410, the paging channels are monitored by the userequipment 170. However, contrary to the CELL_PCH state 408, every cellchange does not trigger a cell update procedure, thus reducingsignalling activity. Instead, an update procedure is launched only if aUTRAN registration area is changed. A state change to the URA_PCH stateis requested by UTRAN if a low activity level of the user equipment 170is detected. The drawback of this arrangement is that the location ofthe user equipment 170 is known with poor accuracy, and the paging areahas to be expanded from one cell to several cells, possibly to a wholeregistration area.

As regards the idle mode in the GSM system, the user equipment 170 isnot allocated any dedicated channel. In a circuit-switched idle mode,the user equipment 170 listens to the common control channel (CCCH) andthe broadcast control channel (BCCH). In packet idle mode, which is onlyapplicable to user equipment supporting GPRS, the user equipment 170 isnot allocated any radio resource on a packet data physical channel.However, the packet common control channel (PCCCH) and the packetbroadcast control channel (PBCCH) or the CCCH and BCCH channels can bereceived by the user equipment 170.

With reference to the flow chart given in FIG. 6, let us consider themethod according to the invention. In start block 600, the radioresource control of the user equipment 170 can be in any state, in whichthe user equipment 170 can camp on the serving cell 310. In block 610,the user equipment 170 camps on the serving cell 310 in an idle state.In block 620, at least one element of the control information 316 forthe cell change procedures is adjusted according to a predetermined timepattern. In block 630, the cell change procedures performed in block650, are controlled. Before performing the cell change procedures, theadjusted control information 316 is received 640 from the network part122 by the user equipment 170. In the stop block, the user equipment 170has finished the cell change procedures, and the radio resource controlcan be in any state. In Block 660, the method is finished.

Referring to the network elements shown in FIGS. 1 and 3 let us examinethe implementation of the method according to the invention. The networkpart 122 comprises control means, such as the base station controller314 of the serving base station 312, for controlling the cell changeprocedures with control information 316. The control information 316includes at least one element that can be used in controlling a specificstep or a function in the cell change procedure.

The network part 122 further comprises adjusting means, such as the basestation controller 314, for adjusting at least one element of saidcontrol information 316 according to the predetermined time pattern,thus forming adjusted control information 316. In an embodiment of theinvention, the adjusting of the control information as well as thecontrolling of the cell change procedures are implemented in the controlunit of the base station controller 314 of the serving base station 312with software applications. The adjusting means, such as base stationcontroller 314, comprises a calendar and a clock, which are monitoredand according to which the control information for controlling the cellchange procedures is adjusted. The adjusting can be performed by loadingpredetermined control information from a memory of the adjusting means.

In a preferred embodiment of the present invention, the adjusting of thecontrol information and the resulting cell change procedures areperformed automatically according to the predetermined time pattern. Ina preferred embodiment of the invention, the serving cell 310 and theneighbour cell 320 are controlled by different base station controllers.

According to the present invention, the control information for the cellchange procedures is adjusted according to a predetermined time pattern.The time pattern comprises time elements which have a characteristicprofile in terms of the state of the mobile communication system. Forinstance, the time element can be a certain time of day, such as day,night, rush hour or a time of a mass event, when the profile of themobile communication system is known a priori at sufficient accuracy.The duration of a time element may vary from minutes to several days orweeks. A long-term time element may be for instance a holiday seasonduring which the load in urban areas is usually lowered. The profileincludes variables, such as an assumed capacity requirement and anassumed cell load, which can be predetermined at a sufficient accuracyfor each time element, and according to which the performance of themobile communication system can be optimised.

In a preferred embodiment of the invention, the time pattern isperiodic, and it is repeated. The duration of a period can be 24 hours,for example, and the period may include several time elements, such asday, night and working hours. As a result, the control information forcontrolling the cell change procedures can be periodic responding to thetime element-specific requirements of the mobile communication system.

In a preferred embodiment of the invention, at least one element of thecontrol information 316 is adjusted based on the assumed capacityrequirement of the mobile communication system. The capacity requirementfor each time element can be determined in the base station controller314 of the serving cell using procedures known by a person skilled inthe art. In an embodiment of the present invention, at least one elementof the control information 316 is adjusted based on an assumed cell loadof the serving cell 310, which can be measured by the network controller314 of the serving cell 310 and according to which appropriate userequipment 170 can be subjected to the cell change procedure according tothe present invention.

In an embodiment of the invention, at least one element of the controlinformation 316 is adjusted according to an assumed difference in cellload between the serving cell 310 and the neighbour cell 320. In suchcase, the control information can be adjusted such that the cell load isbalanced between the two cells 310, 320.

A time variation in the capacity requirements may be caused by a changein the number of the sets of user equipments 170 in the cell system, achange in the location of the user equipments 170, and a change in thecapacity requirement of each user equipment 170. By using the capacityrequirement, capacity in the serving cell 310 can be released, for otherusers by advancing the cell change of the user equipment 170 to anothercell.

In a preferred embodiment of the invention, the time elements aremonitored and the predetermined control information corresponding to atime element is downloaded and used for controlling the cell changeprocedures.

In a preferred embodiment of the invention, at least one element of theidle state control information 316 is adjusted. The idle state controlinformation controls the cell change procedures in idle states only.

With reference to FIGS. 7, 8, and 9 let us consider the embodiments ofthe invention in greater detail. The blocks shown in FIGS. 7, 8, and 9present preferred embodiments of performing the cell change procedurespresented by block 650 in FIG. 6. In a preferred embodiment of theinvention, the target cell is selected based on the adjusted controlinformation, and the user equipment 170 camps on the target cell. Thetarget cell can be selected from a group of cells comprising at leastone neighbour cell 320 and the serving cell 310. Camping on the targetcell can be performed in a similar manner as camping on the serving cell310.

In a preferred embodiment of the invention, the quality of the servingcell 310 and the quality of at least one neighbour cell 320 are measuredby the user equipment 170. Then, the measured cells 310, 320 are rankedbased on the measured quality of the serving cell and the measuredquality of the neighbour cell 320, and the target cell is selected basedon the ranking.

In a preferred embodiment of the invention, at least one qualitythreshold of the serving cell 310 is adjusted, and the quality of theserving cell 310 is measured. Measurements on the neighbour cell 310 aretriggered based on the measured quality of the serving cell 310 and thequality threshold of the serving cell 310, and the target cell isselected based on the triggered measurements.

In a preferred embodiment of the invention, the user equipment 170 campson the serving cell 310 that uses a different carrier frequency fromthat used by the neighbour cell 320. Then at least one inter-frequencymeasurement threshold is adjusted according to the predetermined timepattern. After adjusting, the cell change procedures are performed inthe following manner: measuring the quality of the serving cell 310;triggering inter-frequency measurements on the neighbour cell based onthe measured quality of the serving cell 310 and the inter-frequencymeasurement threshold; and selecting the target cell based on theinter-frequency measurement.

In a preferred embodiment of the invention, the user equipment 170 campson the serving cell 310 that uses a different radio-access technologyfrom that used by the neighbour cell 320. Then the inter-radio accesstechnology measurement threshold is adjusted. After adjusting, the cellchange procedures are performed in a following manner: measuring thequality of the serving cell; triggering inter-radio access technologymeasurements on the neighbour cell based on the measured quality of theserving cell and the inter-radio access technology measurementthreshold; and selecting the target cell based on the inter-radio accesstechnology measurement.

In a preferred embodiment of the invention, at least one qualitythreshold of the neighbour cell 320 is adjusted, and the cell changeprocedures are performed in the following manner: measuring the qualityof the serving cell 310; triggering measurements on the neighbour cell320 based on the measured quality of the serving cell 310; measuringquality of the neighbour cell 320; forming the candidate cell selectionbased on the measured quality of the neighbour cell 320 and the qualitythreshold of the neighbour cell; and selecting the target cell based onthe candidate cell selection.

In a preferred embodiment of the invention, at least one quality offsetof the serving cell 310 is adjusted; and the cell change procedures areperformed in the following manner: measuring the quality of the servingcell 310; applying the quality offset of the serving cell 310 to themeasured quality of the serving cell, thus obtaining an offset-appliedquality of the serving cell 310; measuring the quality of at least oneneighbour cell 320; and selecting the target cell based on the measuredquality of the neighbour cell 320, and the offset-applied quality 520 ofthe serving cell 310.

In a preferred embodiment of the invention, at least one quality offsetof the neighbour cell 320 is adjusted, and the cell change proceduresare performed in the following manner: measuring the quality of theserving cell 310; measuring the quality of at least one neighbour cell320; applying the quality offset of the neighbour cell 320 to themeasured quality of the neighbour cell 320, thus obtaining anoffset-applied quality 550 of the neighbour cell 320; and selecting thetarget cell based on the measured quality of the serving cell 310 andthe offset-applied quality 550 of the neighbour cell 320.

In a preferred embodiment of the invention, at least one temporaryquality offset of the neighbour cell 320 and a penalty time of theneighbour cell are adjusted, and the cell change procedures areperformed in the following manner: measuring the quality of the servingcell 310; measuring 760 the quality of at least one neighbour cell 320;applying the quality offset of the neighbour cell 320 to the measuredquality of the neighbour cell 320 for the duration of the penalty time,thus obtaining a temporary offset-applied quality 564 of the neighbourcell 320; and selecting the target cell based on the measured quality ofthe serving cell 310 and the temporary offset-applied quality 564 of theneighbour cell 320.

With reference to FIG. 5, let us consider in greater detail examples ofembodiments associated with the quality measurements, the qualitythresholds, the quality offsets and the penalty time. In FIG. 5, thevertical axis 502 shows the cell quality in dBm units, for instance. Thehorizontal axis 504 represents a variable, such as time in second units,for instance, which represents the location of the user equipment 170with respect to the serving cell 310 and the neighbour cell 320. Theevolution of the quality of the serving cell 310 and the evolution ofthe corresponding offset-applied quality are represented by curves 510and 520, respectively. The gap 530 between curves 510 and 520 representsthe offset of the quality of the serving cell 310. Curve 514 representsthe scaled quality of the serving cell 310 scaled with a suitablescaling factor 512, such as the minimum required cell quality. Thequality threshold 576 of the serving cell 310 is illustrated withvertical line 576.

Let us follow the evolution of the scaled quality 514 of the servingcell 310. When the scaled quality 514 exceeds the threshold 576 of theserving cell 310, at least one measurement on the neighbour cell 320 istriggered at time point t_(meas1) 570. The measurement comprises atleast one of the following measurements: intra-frequency,inter-frequency, and inter-radio access measurements. According to anembodiment of the invention, the threshold 576 of the quality of theserving cell 310 is adjusted according to the predetermined timepattern. The adjusted threshold is illustrated with dotted line 574,which is shifted from the previous threshold 576. Now, the measurementsare triggered at time point t_(meas2) 572, which is somewhat earlierthan the time point t_(meas1) when the adjusting was not done.Correspondingly, by shifting the threshold in another direction, thetriggering moment can be delayed.

The evolution of the quality of the neighbour cell 320 and the evolutionof the corresponding offset-applied quality are represented by curves540 and 550, respectively. The gap 560 between curves 540 and 550represents the offset of the quality of the neighbour cell 320. Curve544 represents the scaled quality of the neighbour cell 320 scaled witha suitable scaling factor 542, such as the minimum required cellquality. The quality threshold 576 of the neighbour cell 310 isillustrated with vertical line, which in this case coincides with thehorizontal axis 504.

Let us suppose that the measurements in the neighbour cell 320 aretriggered based on, for example, the quality measurements on the servingcell 310. At time point t_(selection1), the scaled quality 544 of theneighbour cell 320 exceeds the quality threshold 504, and the neighbourcell 320 is selected for the candidate cell selection, from which thetarget cell is selected. When the quality threshold 504 of the neighbourcell 320 is adjusted to position indicated with line 578, the neighbourcell 320 is selected for the candidate cell selection at time pointt_(selection2), which is somewhat shifted from the time pointt_(selection1), when the adjusting was not done. In this case, theselection is delayed. However, the selection can be advanced by shiftingthe threshold 578 to the opposite direction from its original value 504.

Let us consider the evolution of the offset-applied quality 520 of theserving cell 310 and the offset-applied quality 550 of the neighbourcell 320, and especially the cross-section of the two curves 520, 550.In an embodiment of the invention, the target cell is selected when theoffset-applied quality 550 of the neighbour cell 310 exceeds theoffset-applied quality 520 of the serving cell 320. The correspondingpoint of time t₁ is shown with pointer 580. In an embodiment of theinvention, the quality offset 530 of the serving cell 310 and thequality offset 550 of the neighbour cell 320 are adjusted. Forsimplicity, both quality offsets 530, 550 are removed, and thus theadjusted offset-applied qualities 530, 550 coincide with theircorresponding measured quality curves 510, 540. Now, the time point forselecting the target cell is t₂ 590, which is advanced from its previousvalue. As a result, the target cell is selected earlier in respect to asituation when the adjusting was not performed.

In an embodiment of the invention, a temporary quality offsetillustrated with indicator 562 is applied to the quality of theneighbour cell 320. The temporary quality offset 562 is applied for theduration of the penalty time 566, which starts, for instance, when thequality of the neighbour cell 320 exceeds a certain threshold. Thetemporary quality offset 562 can be adjusted according to thepredetermined time pattern. The temporary quality offset 562 can beapplied, for instance, to control the selection of the candidate cells.Furthermore, the temporary offset 562 can be applied, when the targetcell is selected from the candidate cell selection.

For the purpose of the cell change procedures, the user equipment 170shall be capable of tuning to the neighbour carriers, from which thesuitable cell is selected. The neighbour cell 320 may belong to adifferent frequency band and to a different radio access technology thanthat used by the serving cell 310. Tuning involves detecting andsynchronizing the user equipment 170 to the neighbour carriers, i.e.carriers employed by the neighbour cell 310. The user equipment 170shall, for example, search all radio frequency channels within its bandsof operation, take readings of received radio frequency signal levels oneach channel, and calculate the signal levels for each. The commonchannel carriers can be identified by searching for frequency correctionbursts, for example.

The list of carriers to be detected may also be signalled to the userequipment 170 on the broadcast channels, such as common pilot channelsand broadcast common channel carrier, and stored in the cellre-selection list of the user equipment 170 for possible later cellre-selection.

In an embodiment of the present invention, the adjusted controlinformation for the cell change procedures is conveyed to the userequipment 170 by means of idle state parameters. The idle stateparameters include: the quality threshold and the quality offset of theserving cell 310, the quality threshold and the quality offset of theneighbour cell 320, the temporary quality offset and the penalty time ofthe neighbour cell 320, and prioritising information.

Let us consider the embodiments of the invention in terms of the 3GPPspecification which defines the idle state parameters for UMTS. In the3GPP specification, the following quantities can be used to representthe cell quality:

a) measured cell Rx level value Q_(rxmeas), which represents thereceived signal code power (RSCP) in UTRAN and GSM carrier receivedsignal strength indicator (RSSI) in GSM. RSCP is determined from theprimary common pilot channel (P-CPICH) ( ) in frequency division duplex(FDD) cells, and from the primary common control physical channel(P-PCPICH) in the time division duplex (TDD) cells. RSSI, respectively,is determined from the GSM broadcast control channel carrier.

b) measured cell quality value Q_(meas) is calculated from the receivedenergy per chip divided by the power density in the band (Ec/No)quantity. Ec/No measurement is performed on the primary common controlchannel.

Furthermore, the following quantities can be used to represent thescaling factors 512 and 542 in UMTS:

a) minimum required Rx level in the cell, indicated by symbolQ_(rxlevmin)

b) minimum required quality level in the cell, indicated by Q_(qualmin)

c) a compensation factor. It can be defined as a difference between themaximum power level that the user equipment 170 uses when accessing thecell in random access channel (RACH) and the maximum output power of theuser equipment 170. The compensation factor is indicated with P_(comp),and its value is always greater than or equal to zero.

The measured qualities and the scaling factors define the followingscaled qualities:

scaled Rx qualityS _(rxlev) =Q _(rxmeas) −Q _(rxlevmin) −P _(comp); and  (1)

scaled qualityS _(qual) =Q _(meas) −Q _(qualmin).  (2)

The quality threshold 576 illustrated in FIG. 5 can represent thefollowing quality thresholds specified in the 3GPP specification:threshold Ss_(earchHCS) is used to control measurement for cellre-selection when the hierarchical cell structure is used. It specifiesthe limit for S_(rxlev) in the serving cell 310, below which the userequipment 170 shall initiate measurements of all neighbour cells 320;threshold S_(HCS,RATm) is used to control measurement for cellre-selection when a hierarchical cell structure is used. It specifiesthe radio access technology-specific threshold in the serving cell 310;parameter S_(intrasearch) specifies the threshold for intra-frequencymeasurements and for the hierarchical cell structure measurement rules;parameter S_(intersearch) specifies the threshold for inter-frequencymeasurements and for the hierarchical cell structure measurement rules;and parameter S_(limit,SearchRATm) is used in the measurement rules forcell re-selection when a hierarchical cell structure is used. Itspecifies the radio access technology-specific threshold in the servingUTRA cell, above which the user equipment 170 need not perform anyinter-radio access technology measurements. The measurement rules arespecified in the 3GPP specification.

The measurement rules listed above can be written in terms ofmathematical notation. In the following, the symbol S_(x) represents thescaled quality 514 of the serving cell 310, i.e. S_(qual) for FDD cells,and S_(rxlev) for TDD and GSM cells.

When a non-hierarchical cell structure is used, the intra-frequencymeasurements are triggered when,S_(intrasearch)<S_(x)≦S_(intersearch).  (3)The intra- and inter-frequency measurements are triggered whenSs_(earchRAT)<S_(x)≦S_(intersearch),  (4)and the inter-radio access technology measurements are triggered when:S_(x)≦S_(searchRAT).  (5)No measurements are initiated whenS_(x)>S_(intrasearch).  (6)

When a hierarchical cell structure is used, the intra- andinter-frequency measurements are initiated on cells with a higherpriority than the serving cell 310 whenSx>S_(intrasearch).  (7)The intra- and inter-frequency measurements are triggered on cells witha higher or equal priority with the serving cell 310 whenS_(x)=S_(intersearch)>S_(intersearch).  (8)All intra-, inter-, and inter-frequency measurements are initiated whenS_(x)=S_(intrasearch)  (9)orS_(rxlev)=S_(searchHCS).  (10)The inter-radio access technology measurements are triggered on cellswith a higher or equal priority whenS_(HCS,RATm)<S_(x)≦S_(limit,SearchRATm).All the inter-radio access technology measurements are triggered when:S_(rxlev)<S_(HCS,RATm)  (11)orS_(qual)<S_(SearchRATm);  (12)However, the inter-radio access technology measurements are not carriedout ifS_(qual)>S_(limit,searchRATm).  (13)

The cell change procedures are carried out if conditions (3)-(13) arefulfilled, and the measurements indicated by the measurement results andthe system information can be initiated.

In TDD cells of UTRAN and the GSM cells, the cell is selected to thecandidate cell selection whenS_(rxlev)>0.  (14)

In FDD cells of UTRAN, the cell is selected to the candidate cellselection whenS_(rxlev)>0 and  (15)S_(qual)>0  (16)simultaneously. In the 3GPP specification, the criteria (14) and (16)are also called the S-criteria. The parameters S_(rxlev) and S_(qual)are defined by Equations (1) and (2) with the exception that the Ec/lor(the received energy per chip divided by the total interference theband) is used instead of CPICH Ec/No in the definition of S_(qual).

Forming the candidate cell selection is followed by a cell reselectionwhere the target cell is chosen from the candidate cell selectionincluding the serving cell 310 by means of relative offsets. When thequality offsets are accounted for, the offset-applied quality parameterscan be defined asR _(s) =Q _(meas,s) +Q _(hyst),  (17)R _(n) =Q _(meas,n) −Q _(offset,n),  (18)wherein Q_(meas,s) and Q_(meas,n) are the measured cell quality of theserving cell 310 and the neighbor cell 320, respectively. The parameterQ_(hyst) is a quality offset of the serving cell 310 and Q_(offset) is aquality offset of the neighbour cell 320. The values of the offsetparameters Q_(hyst) and Q_(offset) are set in the network part (122) andcan be broadcast to the user equipment 170 in system information, forexample.

With further reference to FIG. 5, let us consider an example of a cellchange process based on using the cell quality parameters given inEquations (17) and (18). This case represents a situation, where theserving cell 310 and the neighbour cell 320 belong to different radioaccess technologies, i.e. the cells 310, 320 may use different carrierfrequencies and signal coding. The threshold Ss_(earchRAT) forinter-radio access technology measurements is shown with vertical line576. The evolution of the quality Q_(meas,s) of the serving cell 310 andthe corresponding offset-applied quality R_(s) are represented by curves510 and 520, respectively. The gap 530 between curves 510 and 520represents the quality offset Q_(hyst) of the serving cell. Curve 514represents the scaled cell quality S_(qual,s) of the serving cell 310defined in Equation (2). The gap 512 represents the minimum requiredcell quality Q_(qualmin) used in Equation (2).

When the cell quality criteria S_(qual) exceeds the thresholdS_(interseacrh) 576, the intra-frequency, inter-frequency, andinter-radio access measurements on the neighbour cell 310 are triggered.

The evolution of the quality of the neighbour cell 320 Q_(meas,n) isrepresented by curve 540 whereas the calculated quality parameter R_(s)is represented by curve 550. The gap 560 between curves 540 and 550shows the offset Q_(offset). The cell quality criteria of the neighbourcell S_(qual,n) is represented by curve 544. When the cell qualitycriteria of the neighbour cell S_(qual,n) exceeds zero value at timepoint t_(selection) 546, the neighbour cell is accepted to the candidatecell selection.

Let us consider the evolution of the offset-applied qualities of theserving cell 310 and of the neighbour cell 320 represented by curves 520and 550, respectively. The cell re-selection to the neighbour cell 320takes place when the offset-applied quality Rn of the neighbour cell 310exceeds the offset-applied quality R_(s) of the serving cell 320, i.e.the R_(s) and R_(n) parameters obey relationship R_(n)>R_(s).

Let us consider embodiments of the invention, in which a hierarchicalcell structure 200 shown in FIG. 2 is used. In an embodiment, the userequipment 170 camps on the serving cell 310 belonging to the samehierarchical cell structure 200 as the neighbour cell 320. Then theprioritising information of the hierarchical cell structure 200 isadjusted, and the cells 210 to 270 of the hierarchical cell structure200 are re-prioritised using the adjusted prioritising information. Thenthe cell change procedures are performed based on the re-prioritisinginformation. In an embodiment, the cells 210 to 270 in the hierarchicalcell structure 200 are re-prioritised with equal priorities, and theselection of the target cell can be performed in the same manner as itis carried out in a non-hierarchical cell structure.

With reference to FIGS. 7, 8, and 9 let us consider preferredembodiments of the invention by using a flow chart representation. Inthe start block 700 of FIG. 7, the control information for cell changeprocedures has been received. In block 710, the measurements on thequality of the serving cell 310 are carried out. In block 720, themeasured quality of the serving cell 310 is compared with thecorresponding threshold, and accordingly, the measurements on theneighbour cell 320 are triggered in block 730. In stop block 740, themeasurement on the neighbour cell 320 can be initiated.

In the start block 750 of FIG. 8, the measurements on the neighbour cell320 have been triggered. In block 760, the measurements on the neighbourcell 310 are performed. In block 770, the measured quality of theneighbour cell 320 is compared with the threshold, and accordingly, theneighbour cell 310 is selected to the candidate cell selection in block780. In stop block 790, the target cell can be selected.

In the start block 800 of FIG. 9, the measurements on the serving cell310 and the neighbour cell have been started. In block 810, the qualityoffset 530 of the serving cell 310 is applied to the quality 510 of theserving cell 310. In block 820, the quality offset 560 of the neighbourcell 320 is applied to the quality 540 of the neighbour cell 320. Inblock 830, the temporary offset 562 is applied to the quality 540 of theneighbour cell 320. The order of blocks is 810, 820, and 830 can bevaried, since the measurements and the applying of the offsets can beimplemented independently. In block 840, the cells are ranked. In block850, the target cell is selected and in block 860, the user equipmentcamps on the target cell. In Block 870, the method is finished.According to the invention, the control information controlling thesteps described above can be adjusted according to the predeterminedtime pattern.

FIG. 10 illustrates the structure of a user equipment 170 in such mobilecommunication system to which the solution according to preferredembodiments can be applied. The user equipment 170 comprises an antenna900 for signal transmission and reception. The signal is taken from theantenna 900 to a duplex filter 902, which separates the signals of thetransmission and reception directions from each other. A receiver 904comprises a filter, not shown in FIG. 10, which eliminates thefrequencies outside the desired frequency band. Then, the signal isconverted into an intermediate frequency or directly to base-band, andthe resulting signal is sampled and quantified in an analogue/digitalconverter 906. An equalizer 908 compensates for interference, forinstance the interference caused by multi-path propagation. Ademodulator 910 takes a bit stream from the equalized signal, which bitstream is transmitted to a demultiplexer 912. The demultiplexer 912separates the bit stream into separate logical channels. A channeldecodec 916 decodes the bit stream of different logical channels, i.e.decides whether the bit stream is signalling information to be furthertransmitted to a control unit 918, or whether the bit stream is speechto be further transmitted 920 to a speech codec (not shown). The channelcodec 916 also performs error correction. The control unit 918 performsinternal control tasks by controlling different units. A burst generator922 adds a training sequence and tail bits to the data arriving from thechannel codec 916. A modulator 924 modulates the digital signals to aradio-frequency carrier wave. The nature of this function is analogue,so performing it requires digital/analogue converters 926. A transmitter928 comprises a filter with which the bandwidth is reduced. In addition,the transmitter 928 controls the output power of the transmission. Asynthesizer 930 arranges all required frequencies to different units.The clock contained in the synthesizer 930 can be locally controlled.The synthesizer 930 creates the required frequencies, for example bymeans of a voltage-controlled oscillator.

In the way illustrated by FIG. 7, the structure of the transceiver canbe further divided into radio frequency parts 932 and a digital signalprocessor with software 934. The radio frequency parts 932 comprises areceiver 904, a transmitter 928 and a synthesizer 930. The digitalsignal processor with software 934 comprise an equalizer 908, ademodulator 910, a demultiplexer 912, a channel codec 916, a controlunit 918, a burst generator 922 and a modulator 924. An analogue/digitalconverter 906 is required for converting an analogue radio signal into adigital one, and correspondingly, a digital/analogue converter 926 isrequired for converting a digital signal into an analogue one.

The user equipment 170 is configured to be in connection with more thanone radio system. Typically, this requires that the radio frequencyparts be capable of generating the required frequencies, which may bedifferent in different systems, and that the digital part of theequipment be capable of coding and de-coding the possibly differentsignal forms of different systems.

Further, the equipment may comprise user interface parts, such as adisplay, a keyboard, an earpiece and a microphone. These are not,however, shown in the figure. The control unit 918 of the equipment istypically implemented with a microprocessor or with separate logiccircuits with memory elements, and with required software.

The user equipment 170 comprises receiving means 900, 932, 934 forreceiving signals from the serving base station 320 and from theneighbour base station 322. Furthermore, the user equipment 170comprises cell change procedure means 934 for performing cell changeprocedures based on control information 316 received from the networkpart 122. The cell change procedures can be implemented in the controlunit 918 with suitable software.

In a preferred embodiment of the invention, the cell change procedurescan be controlled so that the probability of a cell change is loweredwhile the user equipment 170 is in a dedicated connection thus reducingmeasurements carried out by the user equipment 170 and signallingbetween the user equipment 170 and the serving base station 310, andincreasing the overall capacity of the mobile communication system,especially in interference-limited radio systems. Especially, the callestablishment success probability for high bit rate services due toenhanced cell re-selection to a cell with a better signal quality isincreased. Furthermore, the embodiments of the invention enable reducedtransmission power of both the serving base station 312 and userequipment 170, thus saving battery consumption of the user equipment170, and increasing capacity in multi-user interference-limitednetworks.

Even though the invention is described above with reference to anexample according to the accompanying drawings, it is clear that theinvention is not restricted thereto but can be modified in several wayswithin the scope of the appended claims.

1. A radio resource control method in a mobile communication systemcomprising a serving cell formed by a serving base station, at least oneneighbour cell formed by a neighbour base station, and user equipmentcapable of receiving signals from said base stations, the methodcomprising: camping, in an idle state, on the serving cell; receiving,in the user equipment, control information for controlling cell changeprocedures of the user equipment, said cell change being conducted fromthe serving cell to a target cell; and performing, in the userequipment, the cell change procedures based on the received controlinformation; adjusting, before the control information is received, atleast one element of said control information according to apredetermined time pattern, thus forming adjusted control information;and controlling the cell change procedures based on said adjustedcontrol information.
 2. The method of claim 1, further comprisingadjusting at least one element of the idle state control information. 3.The method of claim 1, wherein performing the cell change procedurescomprises: selecting the target cell based on the adjusted controlinformation; and camping on the target cell.
 4. The method of claim 1,wherein performing the cell change procedures comprises: measuring thequality of the serving cell; measuring the quality of at least oneneighbour cell; ranking the measured cells based on the measured qualityof the serving cell and the measured quality of the neighbour cell; andselecting the target cell based on the ranking.
 5. The method of claim1, further comprising adjusting at least one quality threshold of theserving cell; and wherein performing the cell change procedurescomprises: measuring the quality of the serving cell; triggeringmeasurements on the neighbour cell based on the measured quality of theserving cell and the quality threshold of the serving cell; andselecting the target cell based on the triggered measurements.
 6. Themethod of claim 1, further comprising: camping on the serving cell thatuses a different carrier frequency from that used by the neighbour cell;adjusting at least one inter-frequency measurement threshold; andwherein performing the cell change procedures comprises: measuring thequality of the serving cell; triggering inter-frequency measurements onthe neighbour cell based on the measured quality of the serving cell andthe inter-frequency measurement threshold; and selecting the target cellbased on the inter-frequency measurement.
 7. The method of claim 1,further comprising: camping on the serving cell that uses a differentradio-access technology from that used by the neighbour cell; adjustingan inter-radio access technology measurement threshold; and whereinperforming the cell change procedures comprises: measuring the qualityof the serving cell; triggering inter-radio access technologymeasurements on the neighbour cell based on the measured quality of theserving cell and the inter-radio access technology measurementthreshold; and selecting the target cell based on the inter-radio accesstechnology measurement.
 8. The method of claim 1, further comprisingadjusting at least one quality threshold of the neighbour cell; andwherein performing, in the user equipment, the cell change procedurescomprises: measuring the quality of the serving cell; triggeringmeasurements on the neighbour cell based on the measured quality of theserving cell; measuring the quality of the neighbour cell; forming thecandidate cell selection based on the measured quality of the neighbourcell and the quality threshold of the neighbour cell; and selecting thetarget cell based on the candidate cell selection.
 9. The method ofclaim 1, further comprising adjusting at least one quality offset of theserving cell; and wherein performing, in the user equipment, the cellchange procedures comprises: measuring the quality of the serving cell,applying the quality offset of the serving cell to the measured qualityof the serving cell, thus obtaining an offset-applied quality of theserving cell; measuring the quality of at least one neighbour cell; andselecting the target cell based on the measured quality of the neighbourcell, and the offset-applied quality of the serving cell.
 10. The methodof claim 1, further comprising adjusting at least one quality offset ofthe neighbour cell; and wherein performing, in the user equipment, thecell change procedures comprises: measuring the quality of the servingcell; measuring the quality of at least one neighbour cell; applying thequality offset of the neighbour cell to the measured quality of theneighbour cell, thus obtaining an offset-applied quality of theneighbour cell; and selecting the target cell based on the measuredquality of the serving cell and the offset-applied quality of theneighbour cell.
 11. The method of claim 1, further comprising adjustingat least one temporary quality offset of the neighbour cell and apenalty time of the neighbour cell; and wherein performing, in the userequipment, the cell change procedures comprises: measuring the qualityof the serving cell; measuring quality of at least one neighbour cell;applying the quality offset of the neighbour cell to the measuredquality of the neighbour cell for the duration of the penalty time, thusobtaining a temporary offset-applied quality of the neighbour cell; andselecting (850) the target cell based on the measured quality of theserving cell and the temporary offset-applied quality of the neighbourcell.
 12. The method of claim 1, further comprising adjusting at leastone element of the control information to assumed capacity requirementsof the mobile communication system.
 13. The method of claim 1, furthercomprising adjusting at least one element of the control informationbased on assumed cell load of the serving cell.
 14. The method of claim1, further comprising: camping, on the serving cell belonging to thesame hierarchical cell structure as the neighbour cell; adjusting theprioritising information of hierarchical cell structure 200;re-prioritising the cells 210 to 270 in a hierarchical cell structure200 using the adjusted prioritising information; and performing the cellchange procedures based on the re-prioritising information.
 15. Themethod of claim 1, further comprising camping in one of the followingidle states specified in the 3GPP specifications: idle mode, CELL_FACHstate, URA_PCH state, CELL_PCH state
 16. The method of claim 1, furthercomprising camping on the serving cell controlled by a base stationcontroller different from the base station controller controlling theneighbour cell.
 17. A mobile communication system, comprising: a networkpart for providing the fixed infrastructure of the mobile communicationsystem, the network part comprising a serving base station for forming aserving cell; and a neighbour base station for forming a neighbour cell;a user equipment comprising receiving means for receiving signals fromthe serving base station and from the neighbour base station; thenetwork part further comprises control means for controlling cell changeprocedures with control information, said cell change being conductedfrom the serving cell to a target cell; the user equipment furthercomprising cell change procedure means for performing cell changeprocedures based on control information received from the network part;wherein the receiving means and cell change procedure means areconfigured to camp on the serving cell in an idle state; and wherein thenetwork part further comprises adjusting means for adjusting at leastone element of said control information according to a predeterminedtime pattern, thus forming adjusted control information.
 18. The mobilecommunication system of claim 17, wherein the adjusting means areconfigured to adjust at least one element of the idle state controlinformation.
 19. The mobile communication system of claim 17, whereinthe cell change procedure means are configured to select the target cellbased on the adjusted control information; and wherein the receivingmeans and the cell change procedure means are configured to camp on thetarget cell.
 20. The mobile communication system of claim 17, whereinthe receiving means and the cell change procedure means are configuredto measure the quality of the serving cell based on the adjusted controlinformation; wherein the receiving means and the cell change proceduremeans are configured to measure the quality of at least one neighbourcell based on the adjusted control information; wherein the cell changeprocedure means are configured to rank the measured cells based on themeasured quality of the serving cell, the measured quality of theneighbour cell, and the adjusted control information; and wherein thecell change procedure means are configured to select the target cellbased on the ranking.
 21. The mobile communication system of claim 17,wherein the adjusting means are configured to adjust at least onequality threshold of the serving cell; wherein the receiving means andthe cell change procedure means are configured to measure the quality ofthe serving cell; wherein the cell change procedure means are configuredto trigger measurements on the neighbour cell based on the measuredquality of the serving cell and the quality threshold of the servingcell; and wherein the cell change procedure means are configured toselect the target cell based on the triggered measurements.
 22. Themobile communication system of claim 17, wherein the receiving means areconfigured to operate at different carrier frequencies; wherein theadjusting means are configured to adjust at least one inter-frequencymeasurement threshold; wherein the receiving means and the cell changeprocedure means are configured to perform inter-frequency measurements;and wherein the cell change procedure means are configured to select thetarget cell based on the inter-frequency measurements.
 23. The mobilecommunication system of claim 17, wherein the receiving means areconfigured to operate with different radio access technologies; andwherein the adjusting means are configured to adjust at least oneinter-radio access technology measurement threshold; wherein thereceiving means and the cell change procedure means are configured toperform inter-radio access technology measurements; and wherein the cellchange procedure means are configured to select the target cell based onthe inter-radio access technology measurements.
 24. The mobilecommunication system of claim 17, wherein the adjusting means areconfigured to adjust at least one quality threshold of the neighbourcell; wherein the receiving means and the cell change procedure meansare configured to measure quality of the serving cell; wherein the cellchange procedure means are configured to trigger measurements on theneighbour cell based on the measured quality of the serving cell;wherein the cell change procedure means and the receiving means areconfigured to measure the quality of the neighbour cell; wherein thecell change procedure means are configured to form the candidate cellselection based on the measured quality of the neighbour cell and thequality threshold of the neighbour cell; and wherein the cell changeprocedure means are configured to select the target cell based on thecandidate cell selection.
 25. The mobile communication system of claim17, wherein the adjusting means are configured to adjust at least onequality offset of the serving cell; wherein the receiving means and thecell change procedure means are configured to measure the quality of theserving cell; wherein the cell change procedure means are configured toapply the quality offset of the serving cell to the measured quality ofthe serving cell, thus producing an offset-applied quality of theserving cell; wherein the cell change procedure means and the receivingmeans are configured to measure the quality of at least one neighbourcell; and wherein the cell change procedure means are configured toselect the target cell based on the measured quality of the neighbourcell, and the offset-applied quality of the serving cell.
 26. The mobilecommunication system of claim 17, wherein the adjusting means areconfigured to adjust at least one quality offset of the neighbour cell;wherein the receiving means and the cell change procedure means areconfigured to measure the quality of the serving cell; wherein the cellchange procedure means and the receiving means are configured to measurethe quality of at least one neighbour cell; wherein the cell changeprocedure means are configured to apply the quality offset of theneighbour cell to the measured quality of the neighbour cell, thusproducing an offset-applied quality of the neighbour cell; and whereinthe cell change procedure means are configured to select the target cellbased on the measured quality of the serving cell, and theoffset-applied quality of the neighbour cell.
 27. The mobilecommunication system of claim 17, wherein the adjusting means areconfigured to adjust at least one temporary quality offset of theneighbour cell and a penalty time of the neighbour cell; wherein thereceiving means and the cell change procedure means are configured tomeasure the quality of the serving cell; wherein the cell changeprocedure means and the receiving means are configured to measure thequality of at least one neighbour cell; wherein the cell changeprocedure means are configured to apply the quality offset of theneighbour cell for the duration of the penalty time to the measuredquality of the neighbour cell, thus producing a temporary offset-appliedquality of the neighbour cell; and wherein the cell change proceduremeans are configured to select the target cell based on the measuredquality of the serving cell, and the temporary offset-applied quality ofthe neighbour cell.
 28. The mobile communication system of claim 17,wherein the adjusting means are configured to adjust at least oneelement of the control information to assumed capacity requirements ofthe mobile communication system.
 29. The mobile communication system ofclaim 17, wherein the adjusting means are configured to adjust at leastone element of the control information based on an assumed cell load inthe serving cell.
 30. The mobile communication system of claim 17,wherein the serving base station and the neighbour base station areconfigured to form a hierarchical cell structure such that the servingcell and the neighbour cell belong to the same hierarchical cellstructure; wherein the adjusting means are configured to adjust theprioritising information; wherein the control means are configured tore-prioritise the serving cell and the neighbour cell based on theadjusted prioritising information; and wherein the cell change proceduremeans are configured to perform the cell change procedures based on there-prioritising.
 31. The mobile communication system of claim 17,wherein the receiving means and cell change procedure means areconfigured to camp on the serving cell in one of the following idlestates specified in the 3GPP specifications: idle mode, CELL_FACH state,URA_PCH state, CELL_PCH state.
 32. The mobile communication system ofclaim 17, wherein the network part comprises separate base stationcontrollers for the serving base station and the neighbour base station.33. A network element of a mobile communication system, which comprises:a serving base station for forming a serving cell; a neighbour basestation for forming a neighbour cell; and a user equipment camped on theserving cell in an idle state and comprising receiving means forreceiving signals from the serving base station and from the neighbourbase station, the user equipment further comprising cell changeprocedure means for performing cell change procedures based on controlinformation; and control means for controlling cell change procedureswith control information, said cell change being conducted from theserving cell to a target cell, the network element further comprisingadjusting means for adjusting at least one element of said controlinformation according to a predetermined time pattern, thus formingadjusted control information.